Thermal sensitive transparency

ABSTRACT

A thermal-sensitive transparency is disclosed. A transparent film substrate is coated with a mixture of a binder and sulfonic acid. A second coating of a binder and a chromogenic compound is applied over the first coating. The binder of the first coating is not soluble in the solvent used to apply the second coating. The thus coated transparency can be imaged in conventional thermal copy machines and used in conventional projection equipment.

United States Patent Glanz et al.

THERMAL SENSITIVE TRANSPARENCY Inventors:

Assignee:

Filed:

Appl. No.:

Kenneth D. Glanz; David B.

McQuain, both of Appleton, Wis.

NCR Corporation, Dayton, Ohio Mar. 20, 1974 Related US. Application DataContinuation-impart of Ser. No. 263,569, June 16,

1972, abandoned.

References Cited UNITED STATES PATENTS Berman 260/326.l1

1 1 Oct. 21, 1975 3,483,013 12/1969 Berg et al. 117/362 3,594,208 7/1971Wiese et al.. 117/368 3.664.858 5/1972 Huffman 117/368 3,666,525 5/1972Kimura et al. 117/368 3.746.675 7/1973 Blose et a1. 117/362 X PrimaryExaminerThomas J. Herbert. Jr. Attorney, Agent, or FirmRobert J. Shafer;E. Frank McKinney [57] ABSTRACT A thermal-sensitive transparency isdisclosed. A transparent film substrate is coated with a mixture of abinder and sulfonic acid. A second coating of a binder and a chromogeniccompound is applied over the first coating. The binder of the firstcoating is not soluble in the solvent used to apply the second coating.The thus coated transparency can be imaged in conventional thermal copymachines and used in conventional projection equipment.

18 Claims, No Drawings THERMAL SENSITIVE TRANSPARENCY This applicationis a continuation-in-part of patent application Ser. No. 263,569, filedJune 16, 1972. now abandoned.

This invention relates to a thermal-sensitive transpar' ent film. Inanother aspect, this invention relates to a method of making such aheat-responsive transparency.

Heat-sensitive record materials are known in the art. Typically,colorless mark-forming components such as crystal violet lactone and aphenolic material are arranged in juxtaposition in a single supportsheet. Application of heat to the sheet causes a migration of theliquefied or vaporized material to a juxtapositioned markformingcomponent to produce a mark, as the markforming components generallyreact upon contact to produce a color. Often, these known heat-sensitivecopy sheets prematurely color before the application of heat. Anotherproblem is the development of color in areas of the sheet where heat isnot applied.

One solution to these problems is disclosed in US. Pat. No. 3,666,525issued May 30, 1972. That patent discloses a support coated with a layerof a spirochromene compound and a solid sulfonic acid in a substancecapable of dissolving the spiro compound and the sulfonic acid whenfused. The patent discloses that when crystal violet lactone orindolinobenzospiropyran compounds are substituted for the spirochromenecompound, the sheet develops a color fog at the time of copy printing.

A thermal-sensitive transparent film now has been developed whichemploys any colorless, but colorable chromogenic compound. Thethermal-sensitive transparency of this invention consists of atransparent film coated with a base coating and a surface coating. Thebase coating is a film formed from a solution containing a film-formingpolymer binder and a sulfonic acid. The base coating is thoroughly driedprior to the coating of the surface coating. The surface coating iscoated from a solution containing a film-forming polymer binder, acolorless but colorable chromogenic compound, and a solvent in which thebinder of the base coating is insoluble.

Accordingly, an object of this invention is to provide athermal-sensitive transparent film.

Another object of this invention is to provide a process for making athermal-sensitive transparent film.

Another object of this invention is to provide a thermal-sensitive filmof decreased background color and increased stability with regard todeveloped hue. It is also an object of this invention to provide aprocess for making such a thermal-sensitive film of decreased backgroundcolor and increased stability.

Other objects, aspects and advantages of this invention will be apparentto one skilled in the art from the following disclosure and appendedclaims.

The transparent substrate employed in this invention can vary widely.Generally, a transparent polymeric film is used. Specific examplesinclude films of cellulose acetate, cellulose acetate butyrate,cellophane, polyester, polyethylene, polystyrene, polyethyleneterephthalate and the like. Preferably, polyethylene terephthalate,polyester or polystyrene is employed. The thickness of the transparentsubstrate varies widely. Generally, the substrate has a thicknessranging from 0.2 to 5 mils.

The base coating is prepared by dissolving a binder and a sulfonic acidin a solvent liquid. The solution then is coated onto the transparentsubstrate by conventional means. Generally, the thickness of the webbase coating ranges from 1 to. 10 mils, preferably 1 to 3 mils. The basecoating then is thoroughly dried prior to the application of the surfacecoating.

Specific solvents used in applying the base coating include water,methanol, ethanol, propano], and the like and mixtures thereof.

The binder employed in the base coating is a film forming polymer whichis insoluble in the volatile organic solvents which are used to applythe surface coating. Specific examples of this binder include polyvinylalcohol, gelatin, polyamide, cellulose nitrate, or polyvinyl butyral andthe like. Polyvinyl alcohol is preferred.

The sulfonic acid employed in this invention is represented by theformula R-SO H wherein R is wherein R is the radical OH, Cl, Cl-l NO orSO H.

Specific examples of the sulfonic acids employed in this inventioninclude:

IO-camphorsulfonic acid;

catechol-3,5-disulfonic acid;

2-chloroaniline-5-sulfonic acid;

2-chloro-6-methylaniline-4-sulfonic acid;

4-chloroaniline-3-sulfonic acid;

m-benzenedisulfonic acid;

p-chlorobenzene sulfonic acid;

2-naphthalenesulfonic acid xylenesulfonic acid;

toluenesulfonic acid;

4-nitrotoluene2-sulfonic acid;

2,4,6-trinitrobenzenesulfonic acid, or

2,4-dinitro-1-naphthol-7-sulfonic acid and the like.

After the base coating has been thoroughly dried, by allowing it tostand for a few minutes or by the application of mild heating or both,the surface coating is pre pared by dissolving a binder and a colorlesschromogenic compound in a volatile organic solvent in which the binderof the base coating is not soluble. If desired, a low melting materialcan be included. Generally, the thickness of the wet surface coatingranges from 1 to mils, preferably 1 to 3 mils. The surface coating isdried prior to use.

The binder employed in the surface coating is a filmforming polymerwhich is soluble in a volatile organic solvent. Specific examples ofthis binder include:

polystyrene;

cellulose acetate butyrate;

polyvinyl acetate;

ethyl hydroxyethyl cellulose;

ethyl cellulose;

polysulfone;

cellulose triacetate;

polyvinyl butyral;

polyvinyl formal;

methyl methacrylate;

styrene copolymer;

dicyclopentadiene resin; or

polyindene resin and the like.

The volatile organic solvents employed in applying the surface coatinginclude toluene, benzene, ethyl acetate, benzene-ethanol mixtures,cyclohexanone, chlorobenzene, methyl ethyl ketone and the like.

Any colorless, but colorable chromogenic compounds can be employed inthe surface coating of this invention. The following examples merelyrepresent a few such compounds:

1. 3,3-spirobi [3fl-naphtho [2,1-b] pyran];

2. 2-decyl-3,3-spirobi [Mi-naphtho [2,l-b] pyran];

3. 2-chloro-3,3'-spirobi [31;l-naphtho [2,l-b] pyran];

4. 2,2-trimethylene-3,3-spirobi [3 l-l-naphtho [2,l-b]

5. 2-n-amyl-3,3'-spirobi [Mi-naphtho [2,l-b] pyran];

6. 2,2-trimethylene-3,3-spirobi [3ll-naphtho [2,l-b]

7. 2,2-trimethylene-2"-methyl-3,3'-spirobi naphtho [2,l-b] pyran];

8. 2-n-heptyl-3,3'-spirobi [3 1-l -naphtho [2,l-b] pyran];

9. 2-isobutyl-3,3-spirobi [3fl-naphtho [2,l-b] pyran];

10. 2-methyl-3,3-spirobi [31;l-naphtho [2,1-b] pyran];

l1. 2-ethyl-3,3'-spirobi [3lj-naphtho [2,l-b] pyran];

12. spiro [21;1-l-benzopyran-2,3-[3l;l]-naphtho [2,1-

13. 2-isopropyl-spiro [21;1-l-benzopyran-2,3-[3l l naphtho [2,l-b]pyran];

l4. 2'-methyl-spiro [2l l-l-benzopyran-2,3'-[3l l]- naphtho [2,1-b]pyran];

15. 2,2-spirobi [2lj-1-benzopyran];

l6. 3 ,3 '-trim ethylene-2,2 -spirobi [21;1-1 -benzopyran];

l7. 2,3-diphenyl-7-methoxy spiro [4ll-l-benzopyran- 4,3'-[3l;l] naphtho[2,l-b] pyran];

18. 2-phenyl-3-methylspiro [4fl- 1 -benzopyran-4,3

[3fl] naphtho [2,l-b] pyran]; l9. 2,2-spirobi [21;1-naphtho [1,2-b]pyran];

20. 2-(2,5-dichloroanilino)-2-(p-methoxyphenyl-2(H) benzopyran);

21. 1',3',3'-trimethyl-8-methoxy spiro[21;1-1-benzopyran-2,2'-indoline]:

22. 1,3,3-trimethylspiro [indoline-2,3'-[31;l]-naphtho 23.1,3,3-trimethylspiro [indoline-2,3-[3fl]-naphtho 24. 3,3-bis(p-dimethylamino dimethylamino phthalide; 25. 3,3-bis(l-ethyl-2-methylindol-3-yl) phthalide;

phenyl )-6- 26. 2'-anilino-6-diethylamino-3'-methylfluoran; or 27.2-methoxy-6-diethylaminofluoran; or 28. 1,3,4'-trimethyl-6'-diethylaminofluoran and the like.

Small amounts of a plasticizer, such as a phthalate like butylbenzylphthalate, can be employed, if desired.

The amounts of materials employed vary widely. The wet base coatinggenerally consists of, by weight, 2.0 to 10.0 percent of the sulfonicacid, 3.0 to 10.0 percent of the binder and 80.0 to 95.0 percent liquid.Preferably, these percentages range from 2.0 to 5.0, 4.0 to 6.0 and 90.0to 95.0 respectively. The wet surface coating generally consists of, byweight, 2.0 to 10.0 percent of the chromogenic compound, 3.0 to 15.0 ofthe binder and 75.0 to 95.0 of the volatile organic solvent. Preferably,these percentages range from 2.0 to 5.0, 5.0 to 10.0 and 85.0 to 93.0,respectively.

In the dry base coating, the ratio by weight of sulfonic acid to thebinder ranges from 1:5 to 3:1, preferably 1:1 to 1:3. 1n the dry surfacecoating, the ratio by weight of the chromogenic compound to the binderranges from 1:8 to 3:1, preferably 1:5 to 1:1.

The coating is allowed to dry and the resulting transparent sheet isready for imaging as follows.

The coated support is now capable of being imaged with heat. The imagecan be produced by contact with a heated surface or by superimposing onan original drawing and heating on any suitable infrared, thermaltransparency maker or copy machine to produce a colored image on atransparent background. The imaged transparency is then ready forprojection in or on conventional projection equipment.

If desired, the base coating and the surface coating can be reverseddepending upon the solvent sensitivity of the transparent film. A threelayer system is also possible with layer containing the chromogeniccompound sandwiched between two layers each containing sulfonic acid.Such a construction will yield a transparency with increased printdensity. Naturally, the binder employed in one coating cannot be solublein the solvent used to apply the next coating. A wide variety of coloredprints are possible depending on the chromogenic compound employed.

The advantages of this invention are further illushated by the followingexamples. The materials and the proportions and other specificconditions are presented as being typical and should not be construed tolimit the invention unduly.

EXAMPLE 1 A transparent polystyrene film substrate was coated asfollows:

A first solution was prepared by dissolving 3.0 grams of polyvinylalcohol, 0.67 grams of IO-camphorsulfonic acid, and 0.67 grams ofZ-naphthalenesulfonic acid in 37 grams of water. The mixture was coatedonto the polystyrene film at a wet thickness of 1 mil. The base coatingwas thoroughyl dried.

A second solution was prepared by dissolving 0.7 grams of polystyrene,0.02 grams of 3,3-spirobi [31inaphtho [2,l-b] pyran], 0.1 grams of2-methyl-3,3'- spirobi [31;l-naphtho [2,1-b] pyran], 0.1 grams of 2-ethyl-3,3-spirobi [3fl-naphtho [2,l-b] pyran], and

0.07 grams of a plasticizer (butylbenzyl phthalate), in 6.3 grams oftoluene. This mixture was coated on top of the base coating at a wetthickness of 1 mil. The coating was thoroughly dried and the resultingtransparent film was imaged on a conventional copying machine. Theimaged film was employed on a conventional overhead projection andprojected a dark blue image on a clear background. No premature coloringor color fogging in unimaged areas was observed.

EXAMPLE II Other thermal-sensitive transparencies were preparedaccording to the procedure described in Example I employing the 28colorless, but colorable chromogenic compounds listed in thespecification. All of these compounds were employed alone and in variousmixtures. However, in the interest of brevity, only a few of theprepared transparencies will be described herein.

Four separate runs were carried out according to the procedure ofExample I except that only one colorless, but colorable compound wasemployed instead of the mixture of Example I. The compound and amountemployed were:

a. 0.2 grams of 2-methyl-3,3-spirobi [3I;I-naphtho l Py b. 0.2 grams of2-ethyl-3,3'-spirobi [31;I-naphtho c. 0.3 grams of2'-anilino-6'-diethylamino-3'- methylfluoran; and

0.2 grams diethylaminotluoran.

Runs (a), (b) and (d) were coated on top of the base coating at awet-thickness of 2 mils, while run (c) was coated at 1 mil as in ExampleI. The amount of polystyrene and toluene in each run was approximatelythe same as in Example I. The base coating was the same as Example I.

After coating and drying, the films each were imaged as in Example I.The imaged films projected a blue, blue, green and orange color,respectively. No premature coloring or color fogging in unimaged areaswas observed.

EXAMPLE III A 2-mil thick transparent film substrate of polyethyleneterephthalate was used as the substrate. A first layer (base coating)composition was prepared by dissolving 3.0 grams of polyvinyl alcohol,1.20 grams of Z-naphthalenesulfonic acid, 0.40 grams of methylatedurea-formaldehyde, and 0.80 grams of bisphenol A, in 17.8 grams ofethanol and 25.0 grams of water.

The polyvinyl alcohol serves as binder for the layer. Any polyvinylalcohol is eligible;--the only requirement being water solubility andformation of a film on drying.

The methylated urea-formaldehyde is a cross-linking agent for thepolyvinyl alcohol and serves to minimize the formation of an undesirablebackground coloration which occurs under certain conditions in theabsence of the cross-linking agent. An eligible methylatedureaformaldehyde is sold by American Cyanamid Co.,

Wayne, New Jersey, under the trademark designation Beetle When theambient conditions at the second coating application are extreme, suchas more than about 50 percent relative humidity and more than aboutFahrenheit, an undesirable background coloration occurs in the absenceof the cross-linking agent. The reason for the effectiveness of acrosslinking agent is not well understood but it is believed that whenthe film which binds the sulfonic acid is crosslinked, there is areduced tendency for reabsorption of atmospheric moisture into the film.Further, it is believed that reabsorbed atmospheric moisture results inpremature generation of color. Generally, any material which cancrosslink the binder is eligible for use herein. In the case ofpolyvinyl alcohol binder, additional eligible crosslinking materialsare, for example: urea-formaldehyde one being that material sold byAmerican Cyanamid Co. under the trademark designation Uracmelamine-formaldehyde-one being that material sold by MonsantoCorporation, St. Louis, Missouri, under the trademark Resloom M-80";polyfunctional aziridine-one being that material sold by Ionac ChemicalCo., Birmingham, New Jersey, under the trademark designation PFAZ-300.The abovenamed, exemplary, crosslinking agents are also effective withbinders such as gelatin, polyvinylbutyral, and the like. Crosslinkingmaterial is generally present at about 0.25 to 3.0 and, preferably,about 1.0 weight percent of the total coating composition. The drycoating weight ratio of crosslinking agent to binder material isgenerally about 1:4 to 1:12 and, preferably, about 1:8.

The bisphenol A (4,4-isopropylidenediphenol) is used to assure colorstability of the thermally developed image. For example, an imagedthermal coating using 2-methyl-3,3'-spirobi [3fl-naphtho [2,l-b] pyran],colorable blue, tends to shift to the red. It has.

been discovered that the addition of a substantial amount of bisphenol Ato the system prevents this shift to the red. Bisphenol H(4,4'-isopropylidene-bis-(2- tertbutylphenol)) can also be used toprevent the red shift by being dissolved in the coating compositionwhich contains the colorless, but colorable chromogenic compound.Bisphenol A or H is generally used at about 1 to 5 and, preferably, 2 to2.5 weight percent of the total coating composition. It should beunderstood that the lower limit, while being largely a matter ofconvenience and efficiency, bears some critical significance in thatbisphenol material levels much below the above minimum do noteffectively prevent the color shift.

The ethanol was added to provide ease of solution but its use isoptional when solution is otherwise accomplished.

The first layer composition was coated onto the substrate film at a wetthickness of about 1 mil and the coating was thoroughly dried.

A second layer (surface coating) composition was prepared by combining0.80 grams of polystyrene-type material, 0.30 grams of2-methyl-3,3-spirobi [3B- naphtho [2,1-b] pyran], 0.045 grams crystalviolet lactone, 0.20 grams chlorobenzene, 0.17 grams of butylbenzylphthalate, and 7.1 grams of toluene. The polystyrene-type materialserves as binder for the layer and can be, for example, astyrene-acrylonitrile copolymer. Polymeric film forming materials,generally, are available; the only requirement being solubility in thesolvent of the composition. An eligible copolymer of styrene andacrylonitrile is sold by The Dow Chemical Company, Midland, Michigan,under the trademark designation Tyril 867.

The chlorobenzene was added to promote solution of the components, thebutylbenzyl phthalate was added as a plasticizer and the use of eitheror both of those components is optional when solution is otherwiseaccomplished and plasticization is not required or desired.

The crystal violet lactone is a weak base added to the system to aid inprevention of background color development. Although its function is notcompletely understood, it is believed that the weak base reacts withresidual sulfonic acid which might find its way to the layer surfaceprior to the imaging'step thereby preventing premature reaction betweenthe sulfonic acid and the chromogenic material. Weak bases are generallyeligible. Secondary amines such as piperazine, piperidine, and the likehave been found to be too strongly basic and are, therefore, ineligible.Tertiary amines which are soluble in the coating composition and whichdo not otherwise create coloration or undesirable side reactions withother layer components, are eligible. Examples of such tertiary aminesinclude dialkylamines such as leucomalachite green,benzoylleucomethylene blue, methane base(bis(pdimethylaminophenyl)methane), methyl-mdiethylaminobenzoate,tribenzylamine, and the like. Weak base material is generally present atabout 0.2 to l and, preferably, 0.4 to 0.6, weight percent of the totalcoating composition. The dry coating weight ratio of chromogenicmaterial to weak base is, preferably, about 6:1.

The second layer composition was coated on top of the dried first layerat a wet thickness of about 1 mi] and the coating was thoroughly dried.The resulting sheet is imaged on a conventional thermal imaging copymachine-and displayed on a conventional transparency projecting devicesuch as a conventional overhead projector. The thermally-developed imageis blue with substantially no background color.

When the cross-linking agent was omitted from the first layer coatingcomposition, and when the second layer coating composition was appliedunder conditions of greater than 50 percent relative humidity andgreater than 80 Fahrenheit without the weak base, a blue backgroundcolor developed over the entire sheet surface. Under those conditions,the addition of either one of the cross-linking agent or the weak basedecreased the development of the, still noticeable, blue backgroundcolor; and addition of both the crosslinking agent and the weak baseeffectively prevented the development of the background color.

When transparency sheets of this Example are made omitting the bisphenolmaterial from the coatings, blue heat-developed images undergoconsiderable shift in hue toward red in only short times. For example,at 90 percent relative humidity and 90 Fahrenheit, images developed fromcoatings made without the bisphenol material suffered a considerable andsubstantial hue shift in less than 8 hours while images developed fromcoatings made including the bisphenol material exhibited no significantshift in more than days. At about 50 percent relative humidity and about70 Fahrenheit, images on coatings without the bisphenol materialexhibited noticeable shift in color after only 30 days while 8 images oncoatings with the bisphenol material were unchanged after more than 1%years.

EXAMPLE IV In this Example, any of the previous Examples are repeatedwith the exception that an additional colorless chromogenic material wasused. The additional colorless chromogenic material was one selected tobe responsive to, and colorable by, ultraviolet light. The amount of theultraviolet light responsive material to be used is from about 10 toweight percent of the amount of the heat responsive chromogenicmaterials. Such amount of ultraviolet light responsive material isgenerally equivalent to about 0.2 to about 15.0 weight percent of thewet coating composition. The ultraviolet light responsive materials arecompounds generally derived from l',3',3'-trimethyl-spiro[2I;I-l-benzopyran- 2,2'-indoline] in especial accordance with thedisclosure of US. Pat. No. 3,100,778, issued Aug. 13, 1963 and aregenerally known as photochromic materials. Eligible photochromiccompounds can also have substitution on the indoline moiety, however,such as chloro, methyl, methoxy and the like. The photochromic materialis dissolved in the coating composition along with the heat-responsivematerial and the composition is applied as a layer, as previouslytaught, above.

Specific examples of coating compositions to make heat and lightresponsive layers in this Example IV include: (a) addition of about 0.3grams of l-phenyl- 3 ',3 -dimethyl-5-bromo-6-nitro-8-methoxy-spiro[21il-benzopyran-2,2-indoline] to each of the heat responsivechromogenic materials disclosed in Example II, above; (b) addition ofabout 0.2 grams of 5'-methyll ,3 ',3 '-trimethyl-6-nitro-spiro [211- l-benzopyran- 2,2-indoline] to the combination of heat responsivechromogenic materials disclosed in Example I, above; and (c) addition ofabout 0.25 grams of 5'-chlorol ,3 ',3'-trimethyl-6-nitro-8-methoxy-spiro [Zfl- 1 benzopyran-2,2'-indoline] tothe heat responsive chromogenic material disclosed in Example III,above. The coating compositions are applied in the same amounts aspreviously disclosed, above; and the resulting transparencies are heatresponsive as previously disclosed, above. The transparencies of thisexample, however, are also imageable by incident ultraviolet light dueto presence of the photochromic material. The photochromic images arereversible and erasable, depending on the photochromic material used,either by permitting fade over a period of time or by exposing theimages to light of wavelength longer than blue to redevelop thecolorless photochromic state. A transparency of this example which hasbeen imaged by heat can be subsequently, repeatedly, imaged byultraviolet light and erased.

Although this invention has been described in considerable detail, itmust be understood that such detail is for the purposes of illustrationonly and that many variations and modifications can be made by oneskilled in the art without departing from the scope and spirit thereof.

What is claimed is:

l. A thermal-sensitive transparent film comprising a transparent filmsubstrate coated with (a) a base coating comprising a binder, acrosslinking agent for the .binder, and at least one sulfonic acidrepresented by the formula wherein R is:

wherein R is the radical OH, Cl, CH;,, NO or SO H, wherein the binder iscrosslinked, and wherein the sulfonic acid and the binder of the basecoating have a ratio of the sulfonic acid to the binder ranging from 1:5to 3:1, and (b) a surface coating comprising a binder which is solublein volatile organic solvents and at least one colorless, but colorablechromogenic compound selected from the group consisting of: 3,3- spirobi[3ll-naphtho [2,1-b] pyran]; 2-decyl-3,3- spirobi [31;1-naphtho [2,1-b]pyran]; 2-chloro-3,3- spirobi [3l;1-naphtho [2,l-b] pyran;2,2'-trimethylene- 3,3'-spirobi [31;i-naphtho [2,1-b] pyran;2-n-amyl-3,3- spirobi [3 ll-naphtho [2,l-b] pyran]; 2,2'-trimethylene-3,3'-spirobi [3l i-naphtho [2,1-b] pyran]; 2,2- trimethylene-2'-methyl-3 3 '-spirobi [3l-i-naphtho [2,l-b] pyran];2-n-heptyl-3,3'-spirobi [3l;I-naphtho [2,1-b] pyran];2-isobutyl-3,3'-spirobi [31;l-naphtho [2,l-b] pyran];2-methyl-3,3-spirobi [3fl-naphtho [2,1-b] pyran]; 2-ethyl-3,3'-spirobi[3li-naphtho [2,lb] pyran]; spiro [2 l- I-1-benzopyran-2,3-[3fl]-naphtho[2,l-b] pyran]; 2'-isopropyl-spiro [Zfld-benzopyran- 2,3'-[3fl]-naphtho[2,l-b] pyran]; 2'-methyl-spiro [2- fl-1-benzopyran-2,3 -[3fi]-naphtho[2,1-b] pyran 2,2-spirobi [Zfll -benzopyran]; 3,3 -trimethylene-2,2-spirobi [Zfi-l-benzopyran]; 2,3-diphenyl-7-methoxy spiro[4fl-1-benzopyran-4,3-[3Il] naphtho [2,1-b] pyran];2-phenyl-3-methylspiro [41-I -1-benzopyran-4,3 [3 l;l naphtho [2,1-b]pyran]; 2,2-spirobi [2gnaphtho [1,2-b] pyran];2-(2,5-dichloroanilino)-2-(pmethoxyphenyl-2(l-I) benzopyran); 1 ',3 ',3'-trimethyl- 8-methoxy spiro [21-1- 1 -b enzopyran-2,2 '-indoline1,3,3-trimethylspiro [indoline-2,3 31-1] -naphtho [2, lb] pyran];1,3,3-trimethylspiro [indoline-2,3-[3fl]- naphtho [2,1-b]-l ,4-oxazine];3 ,3-bis (pdimethylamino phenyl)-6-dimethylaminor phthalide; 3,3-bis(l-ethyl-2-methylindol-3-yl) phthalide; 2- anilino-6 -diethylamino-3-methylfluoran; 2 '-methoxy- 6-dimethylaminofluoran; and l ',3 ',4-trimethyl-6 diethylaminofluoran wherein the chromogenic compound andthe binder of the surface coating have a ratio of the chromogeniccompound to the binder ranging from 1:8 to 3:1, wherein the chromogeniccompound is reacted with the sulfonic acid on heating to form colorwherein the base, coating is sandwiched between the transparent film andthe surface coating, and wherein the binder of the base coating isinsoluble in the volatile organic solvents.

2. A transparent film according to claim 1 wherein the ratio of thesulfonic acid to the binder of the base coating ranges from 1:1 to 1:3,the ratio of crosslinking agent to the binder of the base coating is 1:4to 1:12, and the ratio of the chromogenic compound to the binder of thesurface coating is 1:5 to 1:1.

3. A transparent film according to claim 1 wherein the transparent filmsubstrate is polyester, polyethylene terephthalate or polystyrene.

4. A transparent film according to claim 1 wherein the binder of thebase coating is polyvinyl alcohol and the binder of the surface coatingis a styreneacrylonitrile copolymer or polystyrene.

5. A transparent film according to claim 1 wherein bisphenol A isincluded in the base coating in an amount exceeding one weight percentof the total base coating.

6. A transparent film according to claim 1 wherein bisphenol H isincluded in the surface coating in an amount exceeding one weightpercent of the total surface coating.

7. A transparent film according to claim 1 wherein the surface coatingincludes a tertiary amine weak base.

8. A transparent film according to claim 1 wherein the surface coatingincludes photochromic materialv 9. The transparent film of claim 8wherein the photochromic material is present in an amount 10 to weightpercent of the heat responsive chromogenic material.

11. A process for producing a thermal-sensitive transparent filmconsisting essentially of sequentially:

a. providing a transparent film;

b. coating the transparent film with a wet base coating having athickness ranging from 1 to 10 mils wherein the wet base coatingcomprises, by weight, 2.0 to 10.0 percent of at least one sulfonicrepresented by the formula wherein R is the radical Ol-l, Cl, Cl-l --NOor SO H, 3.0 to 10.0 percent of a binder, 0.25 to 3.0

percent of a cross-linking agent for the binder, and 80.0 to 85.0percent water or alcohol;

c. thoroughly drying the wet base coating and crosslinking the binder;

d. coating the dried base coating with a wet surface coating having athickness ranging from l to 10 mils wherein the wet surface layercomprises, by weight, 2.0 to 10.0 percent of at least one colorless, butcolorable chromogenic compound selected from the group consisting of:3,3-spirobi [3l -l naphtho [2,l-b] pyran]; 2-decyl-3,3'-spirobi[3gnaphtho [2,l-b] pyran]; 2-chloro-3,3'-spirobi [3gnaphtho [2,l-b]pyran]; 2,2-trimethylene-3,3'- spirobi [3fl-naphtho [2,l-b] pyran];2-n-amyl- 3,3'-spirobi [3fl-naphtho [2,1-b] pyran]; 2,2-trimethylene-3,3-spirobi [3fl-naphtho [2,l-b] pyran]; 2,2-trimethylene-2 -methyl-3 ,3 -spirobi [3 li-naphtho [2,l-b] pyran];2-n-heptyl-3,3'- spirobi [3fl-naphtho [2,l-b] pyran]; 2-isobutyl-3,3'-spirobi [3fl-naphtho [2,l-b] pyran]; 2- methyl-3,3'-spirobi[3fl-naphtho [2,l-b] pyran]; 2-ethyl-3,3-spirobi [Fig-naphtho [2,l-b]pyran]; spiro [2l -l l -benzopyran-2,3 '-[3fl[-naphtho [2, l b] pyran];2'-isopropyl-spiro [Zfl-l-benzopyran- 2,3'-[3fl]-naphtho [2,l-b] pyran];2'-methyl-spiro [Zfll -benzopyran-2,3 3fl[-naphtho [2, l -b] pyran];2,2-spirobi [Zfl-l-benzopyran]; 3,3-

trimethylene-2,2 -spirobi [Zfi- 1 -benzopyran 2,3- diphenyl-7-methoxyspiro [4 l;l l -benzopyran-4,3 [3fi] naphtho [2,l-b] pyran]2-phenyl-3-methylspiro [4fl-l-benzopyran-4,3'-[3fl] naphtho [2,lb]pyran]; 2,2-spirobi [Zfl-naphtho [1,2-b] pyran]; 2-( 2,5-dichloroanilino)-2-(p-methoxyphenyl- 2(fl) benzopyran); 1',3',3'-trimethyl-8-methoxyspiro [2H 1 -benzopyran-2,2 '-indoline l ,3,3- trimethylspiro[indoline-2,3 3 ll ]-naphtho [2, lb] pyran]; 1,3,3-trimethylspiro[indoline-2,3- [3fl1-naphtho [2,l-b]-l,4-oxazine]; 3,3-bis(pdimethylamino phenyl)-6-dimethylamino phthalide; 3,3-bis(l-ethyl-2-methylindol-3-yl) phthalide;2'-anilino-6'-diethylamino-3'-methyl-fluoran;2-methoxy-6-diethylaminofluoran; and l',3',4'- trimethyl-6diethylaminofluoran, 3.0 to 15.0 percent of a binder which is soluble involatile organic solvents and 75.0 to 95.0 percent of a volatile organicsolvent; and

thoroughly drying the wet surface'coating, wherein the binder of thebase coating is insoluble in the volatile organic solvents and whereinthe chromogenic compound is reacted with the sulfonic acid on heating toform color.

12. A process according to claim 11 wherein the 7 thickness of the wetbase coating and the wet surface coating each range from 1 to 3 mils andthe wet base coating comprises 2.0 to 5.0 percent of the sulfonic acid,4.0 to 6.0 percent of the binder of the base coating, 0.25 to 3.0percent of the crosslinking agent, and 90.0 to .0 percent of the wateror alcohol and the wet surface coating comprises 2.0 to 5.0 percent ofthe chromogenic compound, 5.0 to 10.0 percent of the binder of thesurface coating and 85.0 to 93.0 of the organic solvent.

13. A process according to claim 11 wherein the binder of the basecoating is polyvinyl alcohol and the binder of the surface coating isstyrene-acrylonitrile copolymer or polystyrene.

14. A processaccording to claim 11 wherein the wet base coatingincludes, by weight, 1 to 5 percent of bisphenol A.

15. A process according to claim 11 wherein the wet surface coatingincludes, by weight, 1 to 5 percent of bisphenol H.

16. A process according to claim 11 wherein the wet surface coatingincludes, by weight, 0.2 to 1 percent of a tertiary amine weak base.

17. A process according to claim 11 wherein the wet surface coatingincludes photochromic material.

18. The process of claim 17 wherein the photochromic material is presentas about 0.2 to about 15.0

weight percent of the wet surface coating.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Q PATENT NO. 3914, 510

DATED I October 21, 1975 INVENTOMS) 1 Kenneth D. Glanz and David B.McQuain it is certified that error appears in the ab0veidentified patentand that said Letters Patent are hereby corrected as shown below:

In Claim 1 at Column 9 line 55, "6"-dimethylaminofluoran;" should be 6-diethylaminof1uoran;-.

In Claim 1 at Column 9, line 61, "base, coating" should be basecoating".

g Signed and Sealed this twenty-fourth Day Of February 1976 [SEAL]Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ojlarentsand Trademarks

1. A THERMAL-SENSITIVE TRANSPARENT FILM COMPRISING A TRANSPARENT FILMSUBSTRATE COATED WITH (A) A BASE COATING COMPRISING A BINDER, ACROSSLINKING FOR THE BINDER, AND AT LEAST ONE SULFONIC ACID REPRESENTEDBY THE FORMULA
 2. A transparent film according to claim 1 wherein theratio of the sulfonic acid to the binder of the base coating ranges from1:1 to 1:3, the ratio of crosslinking agent to the binder of the basecoating is 1:4 to 1:12, and the ratio of the chromogenic compound to thebinder of the surface coating is 1:5 to 1:1.
 3. A transparent filmaccording to claim 1 wherein the transparent film substrate ispolyester, polyethylene terephthalate or polystyrene.
 4. A transparentfilm according to claim 1 wherein the binder of the base coating ispolyvinyl alcohol and the binder of the surface coating is astyrene-acrylonitrile copolymer or polystyrene.
 5. A transparent filmaccording to claim 1 wherein bisphenol A is included in the base coatingin an amount exceeding one weight percent of the total base coating. 6.A transparent film according to claim 1 wherein bisphenol H is includedin the surface coating in an amount exceeding one weight percent of thetotal surface coating.
 7. A transparent film according to claim 1wherein the surface coating includes a tertiary amine weak base.
 8. Atransparent film according to claim 1 wherein the surface coatingincludes photochromic material.
 9. The transparent film of claim 8wherein the photochromic material is present in an amount 10 to 150weight percent of the heat responsive chromogenic material.
 10. Thethermal-sensitive transparent film of claim 1 wherein the binder of thebase coating is polyvinyl alcohol, the cross-linking agent is methylatedurea-formaldehyde, the sulfonic acid is 2-naphthalenesulfonic acid, andthe base-coating also includes bisphenol A; and the binder of thesurface coating is styrene-acrylonitrile copolymer, the colorablechromogenic compound is 2-methyl-3,3''-spirobi (3H-naphtho (2,1-b)pyran), and the surface coating also includes crystal violet lactone.11. A PROCESS FOR PRODUCING A THERMAL-SENSATIVE TRANSPARENT FILMCONSISTING ESSENTIALLY OF SEQUENTIALLY A. PROVIDING A TRANSPARENT FILMB. COATING THE TRANSPARENT FILM WITH A WET BASE COATING HAVING ATHICKNESS RANGING FROM 10 MILS WHEREIN THE WET BASE COATING COMPRISES,BY WEIGHT, 2.0 TO 10.0 PER CENT OF AT LEAST ONE SULFONIC REPRESENTED BYTHE FORMULA R-SO3H WHEREIN R IS R1-PHENYL; R1-NAPHTHYL OR
 12. A processaccording to claim 11 wherein the thickness of the wet base coating andthe wet surface coating each range from 1 to 3 mils and the wet basecoating comprises 2.0 to 5.0 percent of the sulfonic acid, 4.0 to 6.0percent of the binder of the base coating, 0.25 to 3.0 percent of thecrosslinking agent, and 90.0 to 95.0 percent of the water or alcohol andthe wet surface coating comprises 2.0 to 5.0 percent of the chromogeniccompound, 5.0 to 10.0 percent of the binder of the surface coating and85.0 to 93.0 of the organic solvent.
 13. A process according to claim 11wherein the binder of the base coating is polyvinyl alcohol and thebinder of the surface coating is styrene-acrylonitrile copolymer orpolystyrene.
 14. A process according to claim 11 wherein the wet basecoating includes, by weight, 1 to 5 percent of bisphenol A.
 15. Aprocess according to claim 11 wherein the wet surface coating includes,by weight, 1 to 5 percent of bisphenol H.
 16. A process according toclaim 11 wherein the wet surface coating includes, by weight, 0.2 to 1percent of a tertiary amine weak base.
 17. A process according to claim11 wherein the wet surface coating includes photochromic material. 18.The process of claim 17 wherein the photochromic material is present asabout 0.2 to about 15.0 weight percent of the wet surface coating.